PERFORMANCE COMPARISON OF 4x4 BULTER MATRICES DESIGNED WITH STRIPLINE BROADSIDE-COUPLERS AND MICROSTRIP BRANCH-LINE COUPLERS

摘要

This paper presents and compares two realization methods of a 4x4 Bulter matrix for the third-generation mobile communication applications. The first realization method is based on the tri-layer stripline broadside-coupler and the other method uses the microstrip branch-line couplers. The stripline broadside coupler makes use of the tight coupling effect to achieve broadband 3-dB quadrature coupling performance than the branch-line coupler. Therefore, the Bulter matrix based on the broadside coupler has wider bandwidth and takes significantly less size. The measurement results of the broadside-coupled Bulter matrix show that the insertion losses are less than 0.6 dB, amplitude imbalances are within ±0.65 dB, and phase imbalances within ±3° from 1.5 GHz to 2.5 GHz and its size is only 20% of the branch-line-coupler-based Bulter matrix.